The present invention relates to a split torque gear box, and more particularly to an aircraft face gear transmission system.
A transmission system of a rotorcraft or propeller-driven aircraft transfers power from a turbine engine to the rotor or propeller of the rotorcraft or aircraft. A typical proprotor transmission system may direct power from several turbine engines to a single rotor or propeller. Since the rotational velocity of the rotor or propeller is significantly lower than the rotational velocity of the turbine engines, the turbine engine rotational velocity must be reduced by the transmission system. In reducing the rotational velocity of the turbine engine output, torque is increased by the proprotor transmission system through a series of intermediate gear stages and shafts, before the final output drive is provided to the rotor. Relatively large gears are required near the final output drive of the proprotor transmission system to handle the high torque supplied to the rotors.
Many conventional transmission systems include a number of gears arranged for providing split-torque paths. However, conventional split torque transmission systems are somewhat heavy and voluminous. Typically, this is due to the final gears which, although effective, are relatively large and heavy. Additionally, relatively large bearings are required to support the forces generated between the input shafts and face gear which further increases the system weight.
Accordingly, it is desirable to provide a proprotor transmission system, which is relatively small in size and weight, and which minimizes the size of supporting bearings.
The face gear transmission system according to the present invention provides a face gear mounted to an output shaft such as a proprotor shaft which defines a shaft axis of rotation. A first idler face gear and a second idler face gear are coaxially mounted about the shaft axis A. The first and second idler face gears rotate freely relative to the output shaft.
A first input shaft is connected to and driven by a gas turbine engine. The first input shaft drives a second shaft such that the first and second shaft drive the face gear and the first and second idler face gears. A first and second idler serve as crossover gears transferring power from the idler face gears to the face gear.
The present invention divides the input torque from the gas turbine engine into multiple kinematic paths. The first kinematic scheme consists of a drive shaft and driven shaft having a plurality of pinions which contact a primary face gear. The second kinematic scheme consists of two independent symmetrical gear paths. One is a first pinion, a first idler and a first idler face gear and the primary face gear. The other independent gear path is a pinion on the second shaft, the idler, and second idler face gear and the primary face gear. That is, the primary face gear is the only output gear that combines power from all pinions and idlers.
The present invention is especially applicable to rotorcraft having one or more input drive shafts to provide a proprotor transmission system which is relatively small in size and light in weight.